Space Weather Forecasting with Interplanetary Scintillation Data

Map projections

The maps of the sky ('Sky Maps' and 'Sky Sweeps') show the distribution of IPS speed or g-level across the sky as seen from Earth projected onto a planar map. We use two types of projections to convert angular coordinates in the sky to rectangular coordinates in the planar map: 'fish-eye' and Hammer-Aitoff projections. In both types of map the origin of the map of the sky corresponds to the position of the Sun in the sky.

Fish-Eye Projection

This is an example of an azimuthal equidistant projection (or Postel projection) in its polar aspect. The distance to the origin in the planar map is proportional to solar elongation in the sky (defined as the angle between the direction to some position in the sky and the direction to the Sun. This map is useful for heliospheric studies since radial structure (e.g., radial outflow) from the Sun translates to radial structure in the planar map. A disadvantage of this projections that distortions, especially near the poles, are large for elongations larger than 90 degrees, i.e., in the anti-solar hemisphere.

Hammer-Aitoff Projection

The Hammer-Aitoff map is an equal area projection of the sky: areas in the sky with the same area will have the same area in projection on the planar map. This projection also allows mapping of the entire sky without excessive distortions.


The animations illustrate how the sky is projected onto a planar sky map.

The first animation shows a strip of sky at constant elongation as it moves from 0 degrees (the direction to the Sun) to 180 degrees (the anti-solar direction). [click here]

The second animation shows a strip at constant longitude as it moves relative to the Sun from -180 to +180 degrees. [click here]